1. Field Of The Invention
The present invention relates generally to industrial robots, and more particularly to a method and apparatus for controlling the robot so as to perform predetermined operations.
2. Description of The Prior Art
In an industrial robot, generally speaking, a teach-in operation for memorizing the working procedure is accomplished in advance of the actual working operation.
This teach-in operation is usually carried out by manually guiding the working arm of the robot along a desired path on an article to be worked, so as to memorize the working procedure.
After the teach-in operation, the robot accomplishes the playback, that is to say, effects the actual working operation on the article in accordance with the memorized working procedure. In accordance with the kinds of working operations, more specifically, the industrial robot is divided into two type, one of which requires only the location control, and the other of which additionally requires the velocity control. Thus, the operating method of a robot is determined in accordance with the working operations considered.
In one of the most relevant prior art disclosures, for example, U.S. Pat. No. 3,648,143 issued to Harper et al. there is disclosed an arm element articulated at a mounting point externally of a base for movement thereon. The arm is formed of segments articulated at their junctions. A finger is articulated for movement toward and away from the distal arm segment and electrical motors are positioned at each of the articulation points for movement control of the arm segments and the finger element respectively. In operation, the operator places his own arm and finger over the arm segment, and finger. The operator then manipulates or moves the arm segments and finger to perform the function normally performed by the operator in his daily work routine. As the motors are actuated through a worm gear mechanism, the direction, speed, and duration of each rotation of each motor is recorded on tape in the form of a suitable signal. In response to playback of the tape, the motors cause the arm and fingers to perform precisely the functions accomplished when they were secured to the arm and fingers of the operator.
In the case, however, where the location signal and the velocity signal are to be recorded simultaneously, the quality of the playback or actual operation depends upon that of the teach-in operation. For instance, if the operator moves the arm at an instable velocity, the arm will operate at the instable velocity in the actual working operation, too, and this means it is impossible to obtain satisfactory results. In order to obviate this drawback, therefore, there has been proposed a method in which a roller and a drive mechanism are provided at a leading end of the arm when in the teach-in operation so that the roller may be rotated at a predetermined velocity by the driving force of the motor so as to move along a desired path.
Moreover, the velocity control becomes important especially in the case of a welding operation in which a desired velocity along a path is precisely controlled for the parts having a complex construction and shape so as to follow any inclusive curve and to respond to a velocity change in the course of the operation. Since, however, the operating space inherent in the robot is three-dimensional, it has been difficult to detect the linear velocity of the tracing tip of the arm. Thus, a method is conceivable wherein the movements at the respective degrees and freedom of the robot are appropriately considered and the corresponding linear velocity is calculated. This method is, however, found impractical because the calculation formula for the linear velocity takes a complicated form requiring a long calculation time period. This is a result of the fact that the robot has five to seven degrees of freedom, that most of the coordinate systems are cyclindrical or spherical, and that the robot has such an articulated mechanism, using links, as to provide a mutually interfering system.
In place of the complicated calculation method as noted above, another method has also been proposed, in which an equidistantly marked tape is adhered to the desired working path when in the teach-in operation, and in which the location signal finely divided by the teach-in operation at the respective mark points is recorded and reproduced so as to command the preset velocity in each of the finely divided positions. In this method, however, it takes a considerable time period to accomplish such a complicated operation as attachment of the tape. For a path of complex curves, moreover, it is difficult and takes a long time period, to accomplish the working operation. Thus, the second method can neither expect sufficient precision nor be practically suitable.
As seen from the above discussion, a variety of proposals and practices have been found for the location control method for use in an industrial robot. For the attempt to accomplish the location control and the velocity control simultaneously, the conventional control method, which has been proposed, becomes complicated, requires high skills for the actual operation, and takes an increased number of steps due to the difficulty in the velocity control in the case where a high precision is required.